The present invention concerns a micropump with at least two valves and at least one pushing member, while said valves and said pushing members contain which is electrically controlled. A known micropump of the prior art is described in the article "An Electronically Controlled piezoelectric Insulin Pump and Valves." by W. J. Spencer, e.a., IEEE Transactions on Sonics and Ultrasonics, vol SU-25, No 3 May 1978, p153-156.
This known pump of which the stated purpose is the administering of insulin to diabetes patients, has some drawbacks. It is made on the basis of a well known principle, namely the use of an inlet valve and an outlet valve, while said inlet valve and said outlet valve can be opened and closed selectively. The valves and the pushing member are constructed as socalled bimorphs (two polarized piezoelectric elements joined together and mounted between electrodes in such a way, that when an electric voltage is applied, the constellation bends into a concave or convex shape, depending on the polarity of the electric voltage), or as single piezoelectric elements attached to e.g. a metal membrane. Said single piezoelectric elements attached to a metal membrane are called enakemesomorphs. Said enakemesomorphs also have the property that when an electric field is applied to them, while they are in a mechanically stable equilibrium position, e.g. a flat position, they assume a position, deflected from the original equilibrium position, which is either convex or concave, albeit that the deflection is less for a given electric voltage, than that of a bimorph of the same dimensions and containing identical piezoelectric material.
Said pump, hereafter referred to as the Spencer pump, has the disadvantage that special precautions have to be taken to ensure that the valves, which are surrounded by a liquid, are electrically isolated from the liquid to prevent hydrolysis. Further, this pump has been made using conventional assembly techniques, resulting in a pump which is rather large and heavy and unsuitable for implantation in a patient. Moreover, these assembly techniques are not very economical, leading to pumps which are rather expensive.
The present invention has the purpose of providing a means in which small amounts of a liquid or a gas can be pumped from a reservoir into a recipient medium. The liquid could be a medical drug, a coolant or a refrigerant, a fuel in a fuel consuming engine, or a liquid used in a chemical or biological process. Many other applications can be conceived.
The present invention has been stimulated by the need for an implantable insulin pump for diabetes patients, but it has a wider field of application. As the interior of the pump consist of silicon and glass, while the silicon is oxidized, we can state that the parts of the pump which are exposed to the medium which has to be pumped, are hardly or not at all susceptible to corrosion when acids, solvents, or aqueous solutions are present in its interior. Exceptions are some alkaline materials, and hydrogenfluoride, which will etch the silicondioxide and the glass.